The present invention relates to television vectorscopes, and more particularly to a system for automatic generation of vector reference graticules for a vectorscope.
A vectorscope display of a color bar signal is a traditional way of verifying the colorimetric accuracy of a video system. One typical application of this display is for camera adjustment. A user directs the camera to be adjusted at an evenly illuminated color bar chart or an image projected from a transparency, and checks the position of each end-point in the vector display against a reference graticule indicating the theoretically correct positions of the end-points of the respective color vectors. However several complications occur with this technique.
First, it is difficult to control the illumination on the bar chart or through the transparency so that the intensity of the color difference signals (color vectors) matches that of the reference graticule. Most vectorscopes provide for this by allowing the vertical and horizontal gains of the displayed signal to be adjusted.
Second, even after adjusting for variations in illumination there may be colorimetric errors which cannot be fully corrected. For instance the most commonly used phosphors do not allow accurate rendering of all of the colors in the reference vector graticule. Therefore rather than attempting to accurately match the vector signal from the camera to the graticule, some users attempt to match all of their cameras to a known variance from the graticule. Some measurement instruments, such as the 1760 Series Combination Waveform/Vector Monitors manufactured by Tektronix, Inc. of Wilsonville, Oreg., United States of America, provide a set of adjustable vector graticule boxes. The user displays the vector signal from a reference camera, then individually adjusts the phase and magnitude, or alternatively the vertical and horizontal position, of the boxes to match the tips of the color vectors in the displayed signal. This manual adjustment is slow and somewhat tedious.